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            <h1>Node.js v0.10.35 Manual &amp; Documentation</h1>
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          <div id="toc">
            <h2>Table of Contents</h2>
            <ul>
<li><a href="#events_events">Events</a><ul>
<li><a href="#events_class_events_eventemitter">Class: events.EventEmitter</a><ul>
<li><a href="#events_emitter_addlistener_event_listener">emitter.addListener(event, listener)</a></li>
<li><a href="#events_emitter_on_event_listener">emitter.on(event, listener)</a></li>
<li><a href="#events_emitter_once_event_listener">emitter.once(event, listener)</a></li>
<li><a href="#events_emitter_removelistener_event_listener">emitter.removeListener(event, listener)</a></li>
<li><a href="#events_emitter_removealllisteners_event">emitter.removeAllListeners([event])</a></li>
<li><a href="#events_emitter_setmaxlisteners_n">emitter.setMaxListeners(n)</a></li>
<li><a href="#events_emitter_listeners_event">emitter.listeners(event)</a></li>
<li><a href="#events_emitter_emit_event_arg1_arg2">emitter.emit(event, [arg1], [arg2], [...])</a></li>
<li><a href="#events_class_method_eventemitter_listenercount_emitter_event">Class Method: EventEmitter.listenerCount(emitter, event)</a></li>
<li><a href="#events_event_newlistener">Event: &#39;newListener&#39;</a></li>
<li><a href="#events_event_removelistener">Event: &#39;removeListener&#39;</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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          <div id="apicontent">
            <h1>Events<span><a class="mark" href="#events_events" id="events_events">#</a></span></h1>
<pre class="api_stability_4">Stability: 4 - API Frozen</pre><!--type=module-->

<p>Many objects in Node emit events: a <code>net.Server</code> emits an event each time
a peer connects to it, a <code>fs.readStream</code> emits an event when the file is
opened. All objects which emit events are instances of <code>events.EventEmitter</code>.
You can access this module by doing: <code>require(&quot;events&quot;);</code>

</p>
<p>Typically, event names are represented by a camel-cased string, however,
there aren&#39;t any strict restrictions on that, as any string will be accepted.

</p>
<p>Functions can then be attached to objects, to be executed when an event
is emitted. These functions are called <em>listeners</em>. Inside a listener
function, <code>this</code> refers to the <code>EventEmitter</code> that the listener was
attached to.


</p>
<h2>Class: events.EventEmitter<span><a class="mark" href="#events_class_events_eventemitter" id="events_class_events_eventemitter">#</a></span></h2>
<p>To access the EventEmitter class, <code>require(&#39;events&#39;).EventEmitter</code>.

</p>
<p>When an <code>EventEmitter</code> instance experiences an error, the typical action is
to emit an <code>&#39;error&#39;</code> event.  Error events are treated as a special case in node.
If there is no listener for it, then the default action is to print a stack
trace and exit the program.

</p>
<p>All EventEmitters emit the event <code>&#39;newListener&#39;</code> when new listeners are
added and <code>&#39;removeListener&#39;</code> when a listener is removed.

</p>
<h3>emitter.addListener(event, listener)<span><a class="mark" href="#events_emitter_addlistener_event_listener" id="events_emitter_addlistener_event_listener">#</a></span></h3>
<h3>emitter.on(event, listener)<span><a class="mark" href="#events_emitter_on_event_listener" id="events_emitter_on_event_listener">#</a></span></h3>
<p>Adds a listener to the end of the listeners array for the specified <code>event</code>.
No checks are made to see if the <code>listener</code> has already been added. Multiple
calls passing the same combination of <code>event</code> and <code>listener</code> will result in the
<code>listener</code> being added multiple times.

</p>
<pre><code>server.on(&#39;connection&#39;, function (stream) {
  console.log(&#39;someone connected!&#39;);
});</code></pre>
<p>Returns emitter, so calls can be chained.

</p>
<h3>emitter.once(event, listener)<span><a class="mark" href="#events_emitter_once_event_listener" id="events_emitter_once_event_listener">#</a></span></h3>
<p>Adds a <strong>one time</strong> listener for the event. This listener is
invoked only the next time the event is fired, after which
it is removed.

</p>
<pre><code>server.once(&#39;connection&#39;, function (stream) {
  console.log(&#39;Ah, we have our first user!&#39;);
});</code></pre>
<p>Returns emitter, so calls can be chained.

</p>
<h3>emitter.removeListener(event, listener)<span><a class="mark" href="#events_emitter_removelistener_event_listener" id="events_emitter_removelistener_event_listener">#</a></span></h3>
<p>Remove a listener from the listener array for the specified event.
<strong>Caution</strong>: changes array indices in the listener array behind the listener.

</p>
<pre><code>var callback = function(stream) {
  console.log(&#39;someone connected!&#39;);
};
server.on(&#39;connection&#39;, callback);
// ...
server.removeListener(&#39;connection&#39;, callback);</code></pre>
<p><code>removeListener</code> will remove, at most, one instance of a listener from the
listener array. If any single listener has been added multiple times to the
listener array for the specified <code>event</code>, then <code>removeListener</code> must be called
multiple times to remove each instance.

</p>
<p>Returns emitter, so calls can be chained.

</p>
<h3>emitter.removeAllListeners([event])<span><a class="mark" href="#events_emitter_removealllisteners_event" id="events_emitter_removealllisteners_event">#</a></span></h3>
<p>Removes all listeners, or those of the specified event. It&#39;s not a good idea to
remove listeners that were added elsewhere in the code, especially when it&#39;s on
an emitter that you didn&#39;t create (e.g. sockets or file streams).

</p>
<p>Returns emitter, so calls can be chained.

</p>
<h3>emitter.setMaxListeners(n)<span><a class="mark" href="#events_emitter_setmaxlisteners_n" id="events_emitter_setmaxlisteners_n">#</a></span></h3>
<p>By default EventEmitters will print a warning if more than 10 listeners are
added for a particular event. This is a useful default which helps finding memory leaks.
Obviously not all Emitters should be limited to 10. This function allows
that to be increased. Set to zero for unlimited.


</p>
<h3>emitter.listeners(event)<span><a class="mark" href="#events_emitter_listeners_event" id="events_emitter_listeners_event">#</a></span></h3>
<p>Returns an array of listeners for the specified event.

</p>
<pre><code>server.on(&#39;connection&#39;, function (stream) {
  console.log(&#39;someone connected!&#39;);
});
console.log(util.inspect(server.listeners(&#39;connection&#39;))); // [ [Function] ]</code></pre>
<h3>emitter.emit(event, [arg1], [arg2], [...])<span><a class="mark" href="#events_emitter_emit_event_arg1_arg2" id="events_emitter_emit_event_arg1_arg2">#</a></span></h3>
<p>Execute each of the listeners in order with the supplied arguments.

</p>
<p>Returns <code>true</code> if event had listeners, <code>false</code> otherwise.


</p>
<h3>Class Method: EventEmitter.listenerCount(emitter, event)<span><a class="mark" href="#events_class_method_eventemitter_listenercount_emitter_event" id="events_class_method_eventemitter_listenercount_emitter_event">#</a></span></h3>
<p>Return the number of listeners for a given event.


</p>
<h3>Event: &#39;newListener&#39;<span><a class="mark" href="#events_event_newlistener" id="events_event_newlistener">#</a></span></h3>
<div class="signature"><ul>
<li><code>event</code> <span class="type">String</span> The event name</li>
<li><code>listener</code> <span class="type">Function</span> The event handler function</li>
</div></ul>
<p>This event is emitted any time a listener is added. When this event is triggered,
the listener may not yet have been added to the array of listeners for the <code>event</code>.


</p>
<h3>Event: &#39;removeListener&#39;<span><a class="mark" href="#events_event_removelistener" id="events_event_removelistener">#</a></span></h3>
<div class="signature"><ul>
<li><code>event</code> <span class="type">String</span> The event name</li>
<li><code>listener</code> <span class="type">Function</span> The event handler function</li>
</div></ul>
<p>This event is emitted any time someone removes a listener.  When this event is triggered,
the listener may not yet have been removed from the array of listeners for the <code>event</code>.
</p>

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